The present invention related to testing of wafers such as semiconductor wafers for defects and their characterization.
In the production of MEMS, NEMS, or standard semiconductor devices a starting point is a wafer to be processed. The minute constructions produced in such wafers during processing requires that no significant defects exist in the region being processed. The edges of wafers, the region of one to three or five mm from the absolute edge, is prone to defects and is wafer real estate that can nevertheless be used for processing in the absence of defects.
Present day test equipment is not up to the task of providing the needed level of accuracy in testing near their edges. At the edge many of the error sources are also at their worst. Furthermore dimensional variations are significant problems limiting the closeness that a probe can be placed to the wafer under measurement. On the other hand, the narrower the capacitive gap the higher the sensitivity and resolution. Because the edge has a two dimensional variation in shape. The placement of large-area probes that could be used of the surface of the wafer is not practical. The error component of probe signal as the edge also is much higher in level than the signal being sought.